Abstract. We interpret observations from the Intercontinental Chemical Transport
Experiment, Phase B (INTEX-B) in spring 2006 using a global chemical
transport model (GEOS-Chem) to evaluate sensitivities of the free
troposphere above the North Pacific Ocean and North America to Asian
anthropogenic emissions. We develop a method to use satellite observations
of tropospheric NO2 columns to provide timely estimates of trends
in NOx emissions. NOx emissions increased by 33% for China
and 29% for East Asia from 2003 to 2006. We examine measurements from three
aircraft platforms from the INTEX-B campaign, including a Canadian Cessna taking
vertical profiles of ozone near Whistler Peak. The contribution to the mean
simulated ozone profiles over Whistler below 5.5 km is at least 7.2 ppbv for
Asian anthropogenic emissions and at least 3.5 ppbv for global lightning
NOx emissions. Tropospheric ozone columns from OMI exhibit a broad
Asian outflow plume across the Pacific, which is reproduced by simulation.
Mean modelled sensitivities of Pacific (30° N–60° N)
tropospheric ozone columns are at least 4.6 DU for Asian anthropogenic
emissions and at least 3.3 DU for lightning, as determined by simulations
excluding either source. Enhancements of ozone over Canada from Asian
anthropogenic emissions reflect a combination of trans-Pacific transport
of ozone produced over Asia, and ozone produced in the eastern Pacific
through decomposition of peroxyacetyl nitrates (PANs). A sensitivity study
decoupling PANs globally from the model's chemical mechanism establishes that
PANs increase ozone production by removing NOx from regions of low
ozone production efficiency (OPE) and injecting it into regions with higher
OPE, resulting in a global increase in ozone production by 2% in spring 2006.
PANs contribute up to 4 ppbv to surface springtime ozone concentrations in
western Canada. Ozone production due to PAN transport is greatest in the
eastern Pacific; commonly occurring transport patterns advect this ozone
northeastward into Canada. Transport events observed by the aircraft confirm
that polluted airmasses were advected in this way.